Technique for detection of line-of-sight transmissions using millimeter wave communication devices

ABSTRACT

Systems and methods for wireless communications are disclosed. More particularly, aspects of the present disclosure generally relate to techniques for wireless communications by a first apparatus comprising obtaining, via at least first and second receive antennas having different polarizations, first and second training signals transmitted from a second apparatus via at least first and second transmit antennas having different polarizations, determining, based on the first and second training signals, one or more characteristics for different transmit-receive antenna pairs, each pair comprising one of the first or second transmit antennas and one of the first or second receive antennas, and generating, based on one or more characteristics, a parameter indicative of whether a link path between the first and second apparatuses is line of sight (LOS).

CLAIM OF PRIORITY UNDER 35 U.S.C. § 119

The present application for patent claims benefit of U.S. Provisional Patent Application Ser. No. 62/084,111, filed Nov. 25, 2014 and assigned to the assignee hereof and hereby expressly incorporated by reference herein.

TECHNICAL FIELD

Aspects of the present disclosure generally relate to wireless communications and, more particularly, to determining whether wireless devices are in a line of site (LOS) based on training signals transmitted from one of the devices.

BACKGROUND

The 60 GHz band is an unlicensed band which features a large amount of bandwidth and a large worldwide availability overlap. The large bandwidth means that a very high volume of information can be transmitted wirelessly. As a result, multiple applications, each requiring transmission of large amounts of data, can be developed to allow wireless communication around the 60 GHz band. Examples for such applications include, but are not limited to, wireless high definition TV (HDTV), wireless docking stations, wireless Gigabit Ethernet, and many others.

In order to facilitate such applications there is a need to develop integrated circuits (ICs) such as amplifiers, mixers, radio frequency (RF) analog circuits, and active antennas that operate in the 60 GHz frequency range. An RF system typically comprises active and passive modules. The active modules (e.g., a phased array antenna) require control and power signals for their operation, which are not required by passive modules (e.g., filters). The various modules are fabricated and packaged as radio frequency integrated circuits (RFICs) that can be assembled on a printed circuit board (PCB). The size of the RFIC package may range from several to a few hundred square millimeters.

In the consumer electronics market, the design of electronic devices, and thus the design of RF modules integrated therein, should meet the constraints of minimum cost, size, power consumption, and weight. The design of the RF modules should also take into consideration the current assembled configuration of electronic devices, and particularly handheld devices, such as laptop and tablet computers, in order to enable efficient transmission and reception of millimeter wave signals. Furthermore, the design of the RF module should account for minimal power loss of receive and transmit RF signals and for maximum radio coverage.

Operations in the 60 GHz band allow the use of smaller antennas as compared to lower frequencies. However, as compared to operating in lower frequencies, radio waves around the 60 GHz band have high atmospheric attenuation and are subject to higher levels of absorption by atmospheric gases, rain, objects, etc., resulting in higher free space loss. Additionally, radio waves around the 60 GHz band are often reflected by environmental objects. These reflections can change the polarity of the transmissions and this change varies depending on the direction of the polarity of the transmission, as the reflection coefficients for various polarization directions can differ.

This sensitivity to environmental conditions makes determining a link path important. The link path describes the path the radio wave takes between the transmitter and receiver. The link path may include multiple paths such as direct line of sight (LOS), reflection, diffraction, scattering and others. Unlike a radio link in lower frequencies, in a 60 GHz link, reflections are the second dominant mode, right after LOS. Other modes occur significantly less frequently and are rarely selected. Determining whether a LOS connection is desirable because many wireless devices need a way to estimate the distance between a transmitter and receiver. The connection mode influences this measurement because an indirect path may result in a longer measured distance than the actual distance.

Existing techniques for determining the distance include time-of-flight (TOF), estimations of the power-delay-profile (PDP), received power level, and in-room mapping. While these techniques may be sufficient for devices operating in frequencies lower than about seven GHz, these techniques alone are insufficient for transmissions around the 60 GHz band. For example, for the 60 GHz band, the PDP of a reflected path can be similar to that of a non-reflective path. Therefore, a technique for determining whether there is a LOS or non-LOS connection is desired.

SUMMARY

Certain aspects of the present disclosure provide a first apparatus for wireless communications. The apparatus generally includes a first interface for obtaining, via at least first and second receive antennas having different polarizations, first and second training signals transmitted from a second apparatus via at least first and second transmit antennas having different polarizations, and a processing system configured to determine, based on the first and second training signals, one or more characteristics for different transmit-receive antenna pairs, each pair comprising one of the first or second transmit antennas and one of the first or second receive antennas, and generate, based on the characteristics, a line of sight (LOS) parameter indicative of whether a link path between the first and second apparatus is LOS.

Certain aspects of the present disclosure provide a method for wireless communications. The method generally includes obtaining, by a first apparatus, via at least first and second receive antennas having different polarizations, first and second training signals transmitted from a second apparatus via at least first and second transmit antennas having different polarizations, determining, based on the first and second training signals, one or more characteristics for different transmit-receive antenna pairs, each pair comprising one of the first or second transmit antennas and one of the first or second receive antennas, and generating, based on the characteristics, a line of sight (LOS) parameter indicative of whether a link path between the first and second apparatus is LOS.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a diagram of an example wireless communications network, in accordance with certain aspects of the present disclosure.

FIG. 2 illustrates a block diagram of an example access point and user terminals, in accordance with certain aspects of the present disclosure.

FIG. 3 illustrates a block diagram of an example wireless device, in accordance with certain aspects of the present disclosure.

FIG. 4 illustrates an example dual polarized patch element, in accordance with certain aspects of the present disclosure.

FIG. 5 is a diagram illustrating signal propagation in an implementation of phased-array antennas.

FIG. 6 illustrates example operations that may be performed by a wireless device for determining a parameter indicative of line of site (LOS), in accordance with certain aspects of the present disclosure.

FIG. 6A illustrates example components capable of performing the operations shown in FIG. 6.

DETAILED DESCRIPTION

Aspects of the present disclosure provide techniques for determining whether wireless devices are in a line of site (LOS) based on training signals transmitted from one of the devices based on relative gain and/or phase of training signals transmitted from antennas with different polarizations (e.g., horizontal and vertical). Such techniques may provide various advantages over measurements from other techniques and, in some cases, may be used to verify or augment such measurements.

Various aspects of the disclosure are described more fully hereinafter with reference to the accompanying drawings. This disclosure may, however, be embodied in many different forms and should not be construed as limited to any specific structure or function presented throughout this disclosure. Rather, these aspects are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Based on the teachings herein one skilled in the art should appreciate that the scope of the disclosure is intended to cover any aspect of the disclosure disclosed herein, whether implemented independently of or combined with any other aspect of the disclosure. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, the scope of the disclosure is intended to cover such an apparatus or method which is practiced using other structure, functionality, or structure and functionality in addition to or other than the various aspects of the disclosure set forth herein. It should be understood that any aspect of the disclosure disclosed herein may be embodied by one or more elements of a claim.

The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects.

Although particular aspects are described herein, many variations and permutations of these aspects fall within the scope of the disclosure. Although some benefits and advantages of the preferred aspects are mentioned, the scope of the disclosure is not intended to be limited to particular benefits, uses, or objectives. Rather, aspects of the disclosure are intended to be broadly applicable to different wireless technologies, system configurations, networks, and transmission protocols, some of which are illustrated by way of example in the figures and in the following description of the preferred aspects. The detailed description and drawings are merely illustrative of the disclosure rather than limiting, the scope of the disclosure being defined by the appended claims and equivalents thereof.

An Example Wireless Communication System

The techniques described herein may be used for various broadband wireless communication systems, including communication systems that are based on an orthogonal multiplexing scheme. Examples of such communication systems include Orthogonal Frequency Division Multiple Access (OFDMA) systems. An OFDMA system uses orthogonal frequency division multiplexing (OFDM), which is a modulation technique that partitions the overall system bandwidth into multiple orthogonal sub-carriers. These sub-carriers may also be called tones, bins, etc. With OFDM, each sub-carrier may be independently modulated with data. An SC-FDMA system may use interleaved FDMA (IFDMA) to transmit on sub-carriers that are distributed across the system bandwidth, localized FDMA (LFDMA) to transmit on a block of adjacent sub-carriers, or enhanced FDMA (EFDMA) to transmit on multiple blocks of adjacent sub-carriers. In general, modulation symbols are sent in the frequency domain with OFDM and in the time domain with SC-FDMA.

The teachings herein may be incorporated into (e.g., implemented within or performed by) a variety of wired or wireless apparatuses (e.g., nodes). In some aspects, a wireless node implemented in accordance with the teachings herein may comprise an access point or an access terminal.

An access point (“AP”) may comprise, be implemented as, or known as a Node B, a Radio Network Controller (“RNC”), an evolved Node B (eNB), a Base Station Controller (“BSC”), a Base Transceiver Station (“BTS”), a Base Station (“BS”), a Transceiver Function (“TF”), a Radio Router, a Radio Transceiver, a Basic Service Set (“BSS”), an Extended Service Set (“ESS”), a Radio Base Station (“RBS”), or some other terminology.

An access terminal (“AT”) may comprise, be implemented as, or known as a subscriber station, a subscriber unit, a mobile station, a remote station, a remote terminal, a user terminal, a user agent, a user device, user equipment, a user station, or some other terminology. In some implementations, an access terminal may comprise a cellular telephone, a cordless telephone, a Session Initiation Protocol (“SIP”) phone, a wireless local loop (“WLL”) station, a personal digital assistant (“PDA”), a handheld device having wireless connection capability, a Station (“STA”), or some other suitable processing device connected to a wireless modem. Accordingly, one or more aspects taught herein may be incorporated into a phone (e.g., a cellular phone or smart phone), a computer (e.g., a laptop), a portable communication device, a portable computing device (e.g., a personal data assistant), an entertainment device (e.g., a music or video device, or a satellite radio), a global positioning system device, or any other suitable device that is configured to communicate via a wireless or wired medium.

FIG. 1 illustrates a system 100 in which aspects of the disclosure may be performed. For example, the access point 110 or user terminal 120 may determine whether another access point 110 or user terminal 120 is capable of receiving a paging frame (e.g., an ultra low-power paging frame) via a second radio (e.g., a companion radio), while a first radio (e.g., a primary radio) is in a low-power state. The access point 110 or user terminal 120 may generate and transmit the paging frame comprising a command field (e.g., a message ID field) that indicates one or more actions for the other access point 110 or user terminal 120 to take.

The system 100 may be, for example, a multiple-access multiple-input multiple-output (MIMO) system 100 with access points and user terminals. For simplicity, only one access point 110 is shown in FIG. 1. An access point is generally a fixed station that communicates with the user terminals and may also be referred to as a base station or some other terminology. A user terminal may be fixed or mobile and may also be referred to as a mobile station, a wireless device or some other terminology. Access point 110 may communicate with one or more user terminals 120 at any given moment on the downlink and uplink. The downlink (i.e., forward link) is the communication link from the access point to the user terminals, and the uplink (i.e., reverse link) is the communication link from the user terminals to the access point. A user terminal may also communicate peer-to-peer with another user terminal. A system controller 130 may couple to and provide coordination and control for the access point.

A system controller 130 may provide coordination and control for these APs and/or other systems. The APs may be managed by the system controller 130, for example, which may handle adjustments to radio frequency power, channels, authentication, and security. The system controller 130 may communicate with the APs via a backhaul. The APs may also communicate with one another, e.g., directly or indirectly via a wireless or wireline backhaul.

While portions of the following disclosure will describe user terminals 120 capable of communicating via Spatial Division Multiple Access (SDMA), for certain aspects, the user terminals 120 may also include some user terminals that do not support SDMA. Thus, for such aspects, an access point (AP) 110 may be configured to communicate with both SDMA and non-SDMA user terminals. This approach may conveniently allow older versions of user terminals (“legacy” stations) to remain deployed in an enterprise, extending their useful lifetime, while allowing newer SDMA user terminals to be introduced as deemed appropriate.

The access point 110 and user terminals 120 employ multiple transmit and multiple receive antennas for data transmission on the downlink and uplink. For downlink MIMO transmissions, N_(ap) antennas of the access point 110 represent the multiple-input (MI) portion of MIMO, while a set of K user terminals represent the multiple-output (MO) portion of MIMO. Conversely, for uplink MIMO transmissions, the set of K user terminals represent the MI portion, while the N_(ap) antennas of the access point 110 represent the MO portion. For pure SDMA, it is desired to have N_(ap)≥K≥1 if the data symbol streams for the K user terminals are not multiplexed in code, frequency or time by some means. K may be greater than N_(ap) if the data symbol streams can be multiplexed using TDMA technique, different code channels with CDMA, disjoint sets of subbands with OFDM, and so on. Each selected user terminal transmits user-specific data to and/or receives user-specific data from the access point. In general, each selected user terminal may be equipped with one or multiple antennas (i.e., N_(ut)≥1). The K selected user terminals can have the same or different number of antennas.

The system 100 may be a time division duplex (TDD) system or a frequency division duplex (FDD) system. For a TDD system, the downlink and uplink share the same frequency band. For an FDD system, the downlink and uplink use different frequency bands. MIMO system 100 may also use a single carrier or multiple carriers for transmission. Each user terminal may be equipped with a single antenna (e.g., in order to keep costs down) or multiple antennas (e.g., where the additional cost can be supported). The system 100 may also be a TDMA system if the user terminals 120 share the same frequency channel by dividing transmission/reception into different time slots, each time slot being assigned to different user terminal 120.

FIG. 2 illustrates example components of the AP 110 and UT 120 illustrated in FIG. 1, which may be used to implement aspects of the present disclosure. One or more components of the AP 110 and UT 120 may be used to practice aspects of the present disclosure. For example, antenna 224, Tx/Rx 222, processors 210, 220, 240, 242, and/or controller 230 may be used to perform the operations described herein and illustrated with reference to FIGS. 17-18A. Similarly, antenna 252, Tx/Rx 254, processors 260, 270, 288, and 290, and/or controller 280 of the UT 120 may be used to perform the operations described herein and illustrated with reference to FIGS. 5-5A.

FIG. 2 illustrates a block diagram of access point 110 and two user terminals 120 m and 120 x in MIMO system 100. The access point 110 is equipped with N_(t) antennas 224 a through 224 ap. User terminal 120 m is equipped with N_(ut,m) antennas 252 ma through 252 mu, and user terminal 120 x is equipped with N_(ut,x) antennas 252 xa through 252 xu. The access point 110 is a transmitting entity for the downlink and a receiving entity for the uplink. Each user terminal 120 is a transmitting entity for the uplink and a receiving entity for the downlink. As used herein, a “transmitting entity” is an independently operated apparatus or device capable of transmitting data via a wireless channel, and a “receiving entity” is an independently operated apparatus or device capable of receiving data via a wireless channel. In the following description, the subscript “dn” denotes the downlink, the subscript “up” denotes the uplink. For SDMA transmissions, Nup user terminals simultaneously transmit on the uplink, while Ndn user terminals are simultaneously transmit on the downlink by the access point 110. Nup may or may not be equal to Ndn, and Nup and Ndn may be static values or can change for each scheduling interval. The beam-steering or some other spatial processing technique may be used at the access point and user terminal.

On the uplink, at each user terminal 120 selected for uplink transmission, a transmit (TX) data processor 288 receives traffic data from a data source 286 and control data from a controller 280. The controller 208 may be coupled with a memory 282. TX data processor 288 processes (e.g., encodes, interleaves, and modulates) the traffic data for the user terminal based on the coding and modulation schemes associated with the rate selected for the user terminal and provides a data symbol stream. A TX spatial processor 290 performs spatial processing on the data symbol stream and provides N_(ut,m) transmit symbol streams for the N_(ut,m) antennas. Each transmitter unit (TMTR) 254 receives and processes (e.g., converts to analog, amplifies, filters, and frequency upconverts) a respective transmit symbol stream to generate an uplink signal. N_(ut,m) transmitter units 254 provide N_(ut,m) uplink signals for transmission from N_(ut,m) antennas 252 to the access point.

Nup user terminals may be scheduled for simultaneous transmission on the uplink. Each of these user terminals performs spatial processing on its data symbol stream and transmits its set of transmit symbol streams on the uplink to the access point.

At access point 110, N_(ap) antennas 224 a through 224 ap receive the uplink signals from all Nup user terminals transmitting on the uplink. Each antenna 224 provides a received signal to a respective receiver unit (RCVR) 222. Each receiver unit 222 performs processing complementary to that performed by transmitter unit 254 and provides a received symbol stream. An RX spatial processor 240 performs receiver spatial processing on the N_(ap) received symbol streams from N_(ap) receiver units 222 and provides Nup recovered uplink data symbol streams. The receiver spatial processing is performed in accordance with the channel correlation matrix inversion (CCMI), minimum mean square error (MMSE), soft interference cancellation (SIC), or some other technique. Each recovered uplink data symbol stream is an estimate of a data symbol stream transmitted by a respective user terminal. An RX data processor 242 processes (e.g., demodulates, deinterleaves, and decodes) each recovered uplink data symbol stream in accordance with the rate used for that stream to obtain decoded data. The decoded data for each user terminal may be provided to a data sink 244 for storage and/or a controller 230 for further processing. The controller 230 may be coupled with a memory 232

On the downlink, at access point 110, a TX data processor 210 receives traffic data from a data source 208 for Ndn user terminals scheduled for downlink transmission, control data from a controller 230, and possibly other data from a scheduler 234. The various types of data may be sent on different transport channels. TX data processor 210 processes (e.g., encodes, interleaves, and modulates) the traffic data for each user terminal based on the rate selected for that user terminal. TX data processor 210 provides Ndn downlink data symbol streams for the Ndn user terminals. A TX spatial processor 220 performs spatial processing (such as a precoding or beamforming, as described in the present disclosure) on the Ndn downlink data symbol streams, and provides N_(ap) transmit symbol streams for the N_(ap) antennas. Each transmitter unit 222 receives and processes a respective transmit symbol stream to generate a downlink signal. N_(ap) transmitter units 222 providing N_(ap) downlink signals for transmission from N_(ap) antennas 224 to the user terminals.

At each user terminal 120, N_(ut,m) antennas 252 receive the N_(ap) downlink signals from access point 110. Each receiver unit 254 processes a received signal from an associated antenna 252 and provides a received symbol stream. An RX spatial processor 260 performs receiver spatial processing on N_(ut,m) received symbol streams from N_(ut,m) receiver units 254 and provides a recovered downlink data symbol stream for the user terminal. The receiver spatial processing is performed in accordance with the CCMI, MMSE or some other technique. An RX data processor 270 processes (e.g., demodulates, deinterleaves and decodes) the recovered downlink data symbol stream to obtain decoded data for the user terminal. The decoded data for each user terminal may be provided to a data sink 272 for storage and/or a controller 280 for further processing

At each user terminal 120, a channel estimator 278 estimates the downlink channel response and provides downlink channel estimates, which may include channel gain estimates, SNR estimates, noise variance and so on. Similarly, at access point 110, a channel estimator 228 estimates the uplink channel response and provides uplink channel estimates. Controller 280 for each user terminal typically derives the spatial filter matrix for the user terminal based on the downlink channel response matrix Hdn,m for that user terminal Controller 230 derives the spatial filter matrix for the access point based on the effective uplink channel response matrix Hup,eff. Controller 280 for each user terminal may send feedback information (e.g., the downlink and/or uplink eigenvectors, eigenvalues, SNR estimates, and so on) to the access point. Controllers 230 and 280 also control the operation of various processing units at access point 110 and user terminal 120, respectively.

According to certain aspects of the present disclosure, the various processors shown in FIG. 2 may direct the operation at an AP 110 and/or user terminal 120, respectively, to perform various techniques described herein, to determine whether LOS transmissions are utilized based on training signals and/or other processes for the techniques described herein.

FIG. 3 illustrates various components that may be utilized in a wireless device 302 in which aspects of the present disclosure may be practiced and that may be employed within the MIMO system 100. The wireless device 302 is an example of a device that may be configured to implement the various methods described herein. The wireless device 302 may be an access point 110 or a user terminal 120.

The wireless device 302 may include a processor 304 which controls operation of the wireless device 302. The processor 304 may also be referred to as a central processing unit (CPU). Memory 306, which may include both read-only memory (ROM) and random access memory (RAM), provides instructions and data to the processor 304. A portion of the memory 306 may also include non-volatile random access memory (NVRAM). The processor 304 typically performs logical and arithmetic operations based on program instructions stored within the memory 306. The instructions in the memory 306 may be executable to implement the methods described herein. Processor 304 may, for example, perform or direct operations 600 in FIG. 6 to make line of sight determinations, and/or other processes for the techniques described herein.

The wireless device 302 may also include a housing 308 that may include a transmitter 310 and a receiver 312 to allow transmission and reception of data between the wireless device 302 and a remote location. The transmitter 310 and receiver 312 may be combined into a transceiver 314. A single or a plurality of transmit antennas 316 may be attached to the housing 308 and electrically coupled to the transceiver 314. The wireless device 302 may also include (not shown) multiple transmitters, multiple receivers, and multiple transceivers.

The wireless device 302 may also include a signal detector 318 that may be used in an effort to detect and quantify the level of signals received by the transceiver 314. The signal detector 318 may detect such signals as total energy, energy per subcarrier per symbol, power spectral density and other signals. The wireless device 302 may also include a digital signal processor (DSP) 320 for use in processing signals.

The various components of the wireless device 302 may be coupled together by a bus system 322, which may include a power bus, a control signal bus, and a status signal bus in addition to a data bus.

Aspects of the present disclosure may be used to determine whether LOS transmissions are utilized between devices based on training signals. In some cases, the training signals may be transmitted as part of a beamforming (BF) training process (e.g., a beamforming training procedure) according to, for example, the IEEE 802.11ad standard. The BF process is typically employed by a pair of millimeter-wave stations, e.g., a receiver and transmitter. Each pairing of the stations achieves the necessary link budget for subsequent communication among those network devices. As such, BF training is a bidirectional sequence of BF training frame transmissions that uses sector sweep and provides the necessary signals to allow each station to determine appropriate antenna system settings for both transmission and reception. After the successful completion of BF training, a millimeter-wave communication link is established.

The beamforming process solves one of the problems for communication at the millimeter-wave spectrum, which is its high path loss. As such, a large number of antennas are place at each transceiver to exploit the beamforming gain for extending communication range. That is, the same signal is sent from each antenna in an array, but at slightly different times.

According to an exemplary embodiment, the BF process includes a sector level sweep (SLS) phase and a beam refinement stage. In the SLS phase, one of the STAs acts as an initiator by conducting an initiator sector sweep, which is followed by a transmit sector sweep by the responding station (where the responding station conducts a responder sector sweep). A sector is either a transmit antenna pattern or a receive antenna pattern corresponding to a sector ID. As mentioned above, a station may be a transceiver that includes one or more active antennas in an antenna array (e.g., a phased antenna array).

The SLS phase typically concludes after an initiating station receives sector sweep feedback and sends a sector acknowledgement (ACK), thereby establishing BF. Each transceiver of the initiator station and of the responding station is configured for conducting a receiver sector sweep (RXSS) reception of sector sweep (SSW) frames via different sectors, in which a sweep is performed between consecutive receptions and a transmission of multiple sector sweeps (SSW) (TXSS) or directional Multi-gigabit (DMG) beacon frames via different sectors, in which a sweep is performed between consecutive transmissions.

During the beam refinement phase, each station can sweep a sequence of transmissions, separated by a short beamforming interframe space (SBIFS) interval, in which the antenna configuration at the transmitter or receiver can be changed between transmissions. In other words, beam refinement is a process where a station can improve its antenna configuration (or antenna weight vector) both for transmission and reception. That is, each antenna includes an antenna weight vector (AWV), which further includes a vector of weights describing the excitation (amplitude and phase) for each element of an antenna array.

FIG. 4 illustrates a dual polarized patch element 400, in accordance with certain aspects of the present disclosure. As shown in FIG. 4, a single element of an antenna array may contain multiple polarized antennas. Multiple elements may be combined together to form an antenna array. The polarized antennas may be radially spaced. For example, as shown in FIG. 4, two polarized antennas (i.e. dual polarized antenna) may be arranged perpendicularly, corresponding to a horizontally polarized antenna 410 and vertically polarized antenna 420. Alternatively or in addition, any number of polarized antennas may be used. One or both antennas of an element may also be circularly polarized.

FIG. 5 is a diagram illustrating signal propagation 500 in an implementation of phased-array antennas. Phased array antennas use identical elements 510-1 through 510-4 (hereinafter referred to individually as an element 510 or collectively as elements 510). The direction in which the signal is propagated yields approximately identical gain for each element 510, while the phases of the elements 510 are different. Signals received by the elements are combined into a coherent beam with the correct gain in the desired direction. An additional consideration of the antenna design is the expected direction of the electrical field. In case the transmitter and/or receiver are rotated with respect to each other, the electrical field is also rotated in addition to the change in direction. This requires that a phased array be able to handle rotation of the electrical field by using antennas or antenna feeds that match a certain polarity and capable of adapting to other polarity or combined polarity in the event of polarity changes.

Information about signal polarity can be used to determine aspects of the transmitter of the signals. The power of a signal may be measured by different antennas that are polarized in different directions. The antennas may be arranged such that the antennas are polarized in orthogonal directions. For example, a first antenna may be arranged perpendicular to a second antenna where the first antenna represents a horizontal axis and the second antenna represents a vertical axis such that the first antenna is horizontally polarized and the second vertically polarized. Additional antennas may also be included, spaced at various angles in relation to each other. Once the receiver determines the polarity of the transmission the receiver may optimize reception performance by matching the antenna to the received signal.

Example LOS Determination Based on Training Signals

As noted above, aspects of the present disclosure provide techniques for determining relative whether wireless devices are in a line of site (LOS) based on relative gain and/or phase of training signals transmitted from antennas with different polarizations (e.g., horizontal and vertical). The techniques may be applied to any type of device where LOS may be an important factor, such as devices using millimeter wave communications.

FIG. 6 illustrates example operations 600 that may be performed by a wireless device for LOS detection, in accordance with certain aspects of the present disclosure.

Operations 600 begin at 602, by obtaining, via at least first and second receive antennas having different polarizations, first and second training signals transmitted from a second apparatus via at least first and second transmit antennas having different polarizations.

At 604, the wireless device determines, based on the first and second training signals, one or more characteristics for different transmit-receive antenna pairs, each pair comprising one of the first or second transmit antennas and one of the first or second receive antennas.

At 606, the wireless device generates, based on the characteristics, a line of sight (LOS) parameter indicative of whether a link path between the first and second apparatus is LOS.

The operations 600 may be performed by any type of device having a receiver capable of measuring the phase and or gain of such a signal. In some cases, such transmissions and measurements may be done during a beam training phase between a transmitter and receiver.

In some cases, transmitting and receiving only vertically or horizontally polarized signals is inherent in the beam training phases of various standards for millimeter wave communications, such as 802.1 lad, in the sector level sweep (SLS) and beam refinement protocol (BRP) phases. During the BRP training phase using multi-polarization antenna, cross correlations of the transmitted signals may be identified while antennas are switched on and off.

Information about signal polarity may be used to determine aspects of the transmitter of the signals. In certain aspects, the link path between the transmitter and receiver may be determined based on signal polarization. The phase, the gain, or both the phase and gain, may be measured by different antennas that are horizontally or vertically polarized in order to detect an LOS path. For example, in the case of an LOS path, the vertically and horizontally polarized antennas should exhibit substantially identical pathloss from various environmental conditions. Where the transmission is reflected, for example by environmental objects, the vertical and horizontally polarized signals undergo different pathlosses due to varying reflection coefficients.

As a result, a parameter may be calculated based on a measured difference or ratio between the signal received by the horizontally and vertically polarized antenna(s). This parameter may then be compared to a particular threshold. Where the parameter is equal to or above a particular threshold, the signal path may be declared as a non-LOS signal. Where the parameter is below the particular threshold, the signal path may be declared a LOS signal.

In certain aspects, the transmitter sends training signals corresponding to each of a horizontal polarization and a vertical polarization one at a time in a given direction. The receiver then receives the transmissions via horizontally polarized and vertically polarized antennas. Once the receiver finds the average received power for each polarity, the receiver may compare the average received power.

For example, assuming an example where training signals are transmitted using two transmit antennas (horizontal TX-H and vertical TX-V) and a receiver having two receive antennas (horizontal RX-H and vertical RX-V) may generate four characteristics. For example, a first characteristic, r1, may indicate the received signal strength of a transmission from the vertically polarized transmitting antenna, as received on the vertically polarized receiving antenna. As such, each characteristic r1-r4 may be indicative of receive signal strength for each transmit-receive antenna pair, r1-r4, such that: r1=TX-V→RX-V, r2=TX-V→RX-H, r3=TX-H→RX-V, and r4=TX-H→RX-H, where -V describes a vertically polarized signal, -H a horizontally polarized signal, TX describes a transmission, and RX describes a reception.

A parameter may then be generated based on r1 and r4 and/or r2 and r3. Where the parameter indicates that the ratio (or difference) between r1 and r4 and/or r2 and r3 is within a certain threshold (i.e. equal to or less than a threshold value), it may be assumed that there are no substantial reflections in the transmitted training signals and the receiver may determine that there exists a LOS connection between the receiver and the transmitter.

On the other hand, if the ratio (or difference) between the transmission received via the horizontally and vertically polarized antennas exceed a certain threshold, then there is a non-LOS connection. The LOS parameter may also be compared against a second parameter generated to verify the results. For example, when the LOS parameter is calculated based on r1 and r4, this second parameter may be calculated based on r2 and r3, or based on a different technique altogether.

In certain aspects, the thresholds or signals may be adjusted based on various factors to compensated for various environmental conditions. These factors may include known factors such as a cross-polarization number, or polarization coefficients, antennas used, signal to noise ratio, or any other known factor. These factors may be transmitted by the transmitter device. The receiver may receive an indication of these factors and use these factors to adjust the thresholds. Alternatively, the receiver may calculate, lookup, or otherwise obtain these factors without reference to the transmitter. According to certain aspects, different techniques for calculating LOS may be combined to make an LOS determination. For example, in some cases, LOS calculated based on training signals may be used to verify an LOS determination made by conventional means, such as PDP. As another example, an LOS parameter, calculated as described herein, may also be combined with determinations made by conventional means to further refine the LOS determination.

In certain aspects, after the receiver generates a LOS parameter, outputting the LOS parameter for transmission to the transmitter. The transmitter may also use this received LOS parameter to make a LOS determination, by, for example, comparing the LOS parameter to a certain threshold which may or may not be the same threshold used by the receiver.

In certain aspects, the determination as to whether LOS between a transmitter and receiver exists may be transmitted back to the transmitter by the receiver as a part of positioning information. Additionally, LOS information may be passed up to an application layer, for example, for use by an application to help optimize reception between the transmitter and receiver.

The various operations of methods described above may be performed by any suitable means capable of performing the corresponding functions. The means may include various hardware and/or software component(s) and/or module(s), including, but not limited to a circuit, an application specific integrated circuit (ASIC), or processor. Generally, where there are operations illustrated in figures, those operations may have corresponding counterpart means-plus-function components with similar numbering. For example, operations 600 illustrated in FIG. 6 correspond to means 600A illustrated in FIG. 6A.

Means for obtaining (e.g., receiving) may comprise a receiver (e.g., the receiver unit 254) and/or an antenna(s) 252 of the UT 120 illustrated in FIG. 2 or the receiver 312 and/or antenna(s) 316 depicted in FIG. 3. Means for transmitting and means for outputting may be a transmitter (e.g., the transmitter unit of transceiver 254) and/or an antenna(s) 252 of the user terminal 120 illustrated in FIG. 2 or the transmitter (e.g., the transmitter unit of transceiver 222) and/or antenna(s) 224 of access point 110 illustrated in FIG. 2.

Means for generating, means for detecting, means for determining, means for obtaining, means for selecting, means for adjusting, means for processing, means for indicating, and/or means for applying may include a processing system, which may include one or more processors such as processors 260, 270, 288, and 290 and/or the controller 280 of the UT 120 or the processor 304 and/or the DSP 320 portrayed in FIG. 3.

In some cases, rather than actually transmitting a frame a device may have an interface to output a frame for transmission. For example, a processor may output a frame, via a bus interface, to a radio frequency (RF) front end for transmission. Similarly, rather than actually receiving a frame, a device may have an interface to obtain a frame received from another device. For example, a processor may obtain (or receive) a frame, via a bus interface, from an RF front end for reception.

According to certain aspects, such means may be implemented by processing systems configured to perform the corresponding functions by implementing various algorithms (e.g., in hardware or by executing software instructions) described above for determining the presence of a LOS transmission.

As used herein, the term “determining” encompasses a wide variety of actions. For example, “determining” may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database or another data structure), ascertaining and the like. Also, “determining” may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory) and the like. Also, “determining” may include resolving, selecting, choosing, establishing and the like.

As used herein, a phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover a, b, c, a-b, a-c, b-c, and a-b-c, as well as any combination with multiples of the same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b, b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c).

The various illustrative logical blocks, modules and circuits described in connection with the present disclosure may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device (PLD), discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any commercially available processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps of a method or algorithm described in connection with the present disclosure may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in any form of storage medium that is known in the art. Some examples of storage media that may be used include random access memory (RAM), read only memory (ROM), flash memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM and so forth. A software module may comprise a single instruction, or many instructions, and may be distributed over several different code segments, among different programs, and across multiple storage media. A storage medium may be coupled to a processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor.

The methods disclosed herein comprise one or more steps or actions for achieving the described method. The method steps and/or actions may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is specified, the order and/or use of specific steps and/or actions may be modified without departing from the scope of the claims.

The functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in hardware, an example hardware configuration may comprise a processing system in a wireless node. The processing system may be implemented with a bus architecture. The bus may include any number of interconnecting buses and bridges depending on the specific application of the processing system and the overall design constraints. The bus may link together various circuits including a processor, machine-readable media, and a bus interface. The bus interface may be used to connect a network adapter, among other things, to the processing system via the bus. The network adapter may be used to implement the signal processing functions of the PHY layer. In the case of a user terminal 120 (see FIG. 1), a user interface (e.g., keypad, display, mouse, joystick, etc.) may also be connected to the bus. The bus may also link various other circuits such as timing sources, peripherals, voltage regulators, power management circuits, and the like, which are well known in the art, and therefore, will not be described any further.

The processor may be responsible for managing the bus and general processing, including the execution of software stored on the machine-readable media. The processor may be implemented with one or more general-purpose and/or special-purpose processors. Examples include microprocessors, microcontrollers, DSP processors, and other circuitry that can execute software. Software shall be construed broadly to mean instructions, data, or any combination thereof, whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. Machine-readable media may include, by way of example, RAM (Random Access Memory), flash memory, ROM (Read Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable Programmable Read-Only Memory), EEPROM (Electrically Erasable Programmable Read-Only Memory), registers, magnetic disks, optical disks, hard drives, or any other suitable storage medium, or any combination thereof. The machine-readable media may be embodied in a computer-program product. The computer-program product may comprise packaging materials.

In a hardware implementation, the machine-readable media may be part of the processing system separate from the processor. However, as those skilled in the art will readily appreciate, the machine-readable media, or any portion thereof, may be external to the processing system. By way of example, the machine-readable media may include a transmission line, a carrier wave modulated by data, and/or a computer product separate from the wireless node, all which may be accessed by the processor through the bus interface. Alternatively, or in addition, the machine-readable media, or any portion thereof, may be integrated into the processor, such as the case may be with cache and/or general register files.

The processing system may be configured as a general-purpose processing system with one or more microprocessors providing the processor functionality and external memory providing at least a portion of the machine-readable media, all linked together with other supporting circuitry through an external bus architecture. Alternatively, the processing system may be implemented with an ASIC (Application Specific Integrated Circuit) with the processor, the bus interface, the user interface in the case of an access terminal), supporting circuitry, and at least a portion of the machine-readable media integrated into a single chip, or with one or more FPGAs (Field Programmable Gate Arrays), PLDs (Programmable Logic Devices), controllers, state machines, gated logic, discrete hardware components, or any other suitable circuitry, or any combination of circuits that can perform the various functionality described throughout this disclosure. Those skilled in the art will recognize how best to implement the described functionality for the processing system depending on the particular application and the overall design constraints imposed on the overall system.

The machine-readable media may comprise a number of software modules. The software modules include instructions that, when executed by the processor, cause the processing system to perform various functions. The software modules may include a transmission module and a receiving module. Each software module may reside in a single storage device or be distributed across multiple storage devices. By way of example, a software module may be loaded into RAM from a hard drive when a triggering event occurs. During execution of the software module, the processor may load some of the instructions into cache to increase access speed. One or more cache lines may then be loaded into a general register file for execution by the processor. When referring to the functionality of a software module below, it will be understood that such functionality is implemented by the processor when executing instructions from that software module.

If implemented in software, the functions may be stored or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media include both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage medium may be any available medium that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared (IR), radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, include compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Thus, in some aspects computer-readable media may comprise non-transitory computer-readable media (e.g., tangible media). In addition, for other aspects computer-readable media may comprise transitory computer-readable media (e.g., a signal). Combinations of the above should also be included within the scope of computer-readable media.

Thus, certain aspects may comprise a computer program product for performing the operations presented herein. For example, such a computer program product may comprise a computer-readable medium having instructions stored (and/or encoded) thereon, the instructions being executable by one or more processors to perform the operations described herein. For certain aspects, the computer program product may include packaging material.

Further, it should be appreciated that modules and/or other appropriate means for performing the methods and techniques described herein can be downloaded and/or otherwise obtained by a user terminal and/or base station as applicable. For example, such a device can be coupled to a server to facilitate the transfer of means for performing the methods described herein. Alternatively, various methods described herein can be provided via storage means (e.g., RAM, ROM, a physical storage medium such as a compact disc (CD) or floppy disk, etc.), such that a user terminal and/or base station can obtain the various methods upon coupling or providing the storage means to the device. Moreover, any other suitable technique for providing the methods and techniques described herein to a device can be utilized.

It is to be understood that the claims are not limited to the precise configuration and components illustrated above. Various modifications, changes and variations may be made in the arrangement, operation and details of the methods and apparatus described above without departing from the scope of the claims. 

What is claimed is:
 1. A first apparatus for wireless communications, comprising: a first interface for obtaining, via at least first and second receive antennas having different polarizations, first and second training signals transmitted from a second apparatus via at least first and second transmit antennas having different polarizations; a processing system configured to: determine, based on the first and second training signals, at least first and second characteristics for different transmit-receive antenna pairs, each pair comprising one of the first or second transmit antennas and one of the first or second receive antennas, and generate, based on a difference or a ratio between the first and second characteristics, a parameter indicative of whether a link path between the first and second apparatuses is line of sight (LOS), wherein the first characteristic is determined based on the first training signal and the second characteristic is determined based on the second training signal; and a second interface for outputting the parameter for transmission to the second apparatus.
 2. The first apparatus of claim 1, wherein the first and second characteristics comprise receive power of training signals transmitted and received via a given one of the transmit-receive antenna pairs.
 3. The first apparatus of claim 1, wherein the first and second characteristics comprise receive phase of training signals transmitted and received via a given one of the transmit-receive antenna pairs.
 4. The first apparatus of claim 1, wherein: the first characteristic is determined based on the first training signal as received on the first receive antenna; and the second characteristic is determined based on the second training signal as received on the second receive antenna.
 5. The first apparatus of claim 4, wherein the processing system is configured to indicate, via the parameter, that the link path between the first and second apparatuses is LOS if the difference or the ratio between the first and second characteristics is equal to or below a threshold value.
 6. The first apparatus of claim 5, wherein the first and second characteristics and the threshold value are adjusted based on a factor.
 7. The first apparatus of claim 6, wherein the factor is based on at least one of a cross-polarization number or polarization coefficients.
 8. The first apparatus of claim 6, wherein the factor is based on at least an indication received from the second apparatus.
 9. The first apparatus of claim 4, wherein: the first characteristic is determined based on the first training signal as received on the second receive antenna; and the second characteristic is determined based on the second training signal as received on the first receive antenna.
 10. The first apparatus of claim 9, wherein the processing system is configured to indicate, via the parameter, that the link path between the first and second apparatuses is LOS if the difference or the ratio between the first and second characteristics is equal to or below a threshold value.
 11. The first apparatus of claim 1, wherein the first and second training signals are received as a part of a beamforming training procedure.
 12. The first apparatus of claim 1, wherein: the different polarizations of the first and second transmit antennas correspond to horizontal and vertical polarizations.
 13. The first apparatus of claim 1, wherein: the different polarizations of the first and second receive antennas correspond to horizontal and vertical polarizations.
 14. The first apparatus of claim 1, wherein: at least the first and second receive and transmit antennas comprise a dual polarized antenna.
 15. The first apparatus of claim 1, wherein at least one of the first or second antenna is circularly polarized.
 16. A method for wireless communications by a first apparatus, comprising: obtaining, via at least first and second receive antennas having different polarizations, first and second training signals transmitted from a second apparatus via at least first and second transmit antennas having different polarizations; determining, based on the first and second training signals, at least first and second characteristics for different transmit-receive antenna pairs, each pair comprising one of the first or second transmit antennas and one of the first or second receive antennas; generating, based on a difference or a ratio between the first and second characteristics, a parameter indicative of whether a link path between the first and second apparatuses is line of sight (LOS), wherein the first characteristic is determined based on the first training signal and the second characteristic is determined based on the second training signal; and outputting the parameter for transmission to the second apparatus.
 17. The method of claim 16, wherein the first and second characteristics comprise receive power of training signals transmitted and received via a given one of the transmit-receive antenna pairs.
 18. The method of claim 16, wherein the first and second characteristics comprise receive phase of training signals transmitted and received via a given one of the transmit-receive antenna pairs.
 19. The method of claim 16, wherein: the first characteristic is determined based on the first training signal as received on the first receive antenna; and the second characteristic is determined based on the second training signal as received on the second receive antenna.
 20. The method of claim 16, wherein the first and second training signals are received as a part of a beamforming training procedure.
 21. The method of claim 16, wherein: the different polarizations of the first and second transmit antennas correspond to horizontal and vertical polarizations.
 22. The method of claim 16, wherein: the different polarizations of the first and second receive antennas correspond to horizontal and vertical polarizations.
 23. A first apparatus for wireless communications, comprising: means for obtaining, via at least first and second receive antennas having different polarizations, first and second training signals transmitted from a second apparatus via at least first and second transmit antennas having different polarizations; means for determining, based on the first and second training signals, at least first and second characteristics for different transmit-receive antenna pairs, each pair comprising one of the first or second transmit antennas and one of the first or second receive antennas; means for generating, based on a difference or a ratio between the first and second characteristics, a parameter indicative of whether a link path between the first and second apparatuses is line of sight (LOS), wherein the first characteristic is determined based on the first training signal and the second characteristic is determined based on the second training signal; and means for outputting the parameter for transmission to the second apparatus.
 24. A wireless station, comprising: at least first and second receive antennas having different polarizations; a receiver for receiving, via the first and second receive antennas, first and second training signals transmitted from an apparatus via at least first and second transmit antennas having different polarizations; and a processing system configured to: determine, based on the first and second training signals, at least first and second characteristics for different transmit-receive antenna pairs, each pair comprising one of the first or second transmit antennas and one of the first or second receive antennas, generate, based on a difference or a ratio between the first and second characteristics, a parameter indicative of whether a link path between the wireless station and the apparatus is line of sight (LOS), wherein the first characteristic is determined based on the first training signal and the second characteristic is determined based on the second training signal; and a transmitter configured to transmit the parameter to the apparatus.
 25. The wireless station of claim 24, wherein the first and second receive antennas comprise at least one vertically polarized receive antenna and at least one horizontally polarized receive antenna.
 26. The method of claim 16, wherein: the first characteristic is determined based on the first training signal as received on the second receive antenna; and the second characteristic is determined based on the second training signal as received on the first receive antenna.
 27. The method of claim 16, further comprising indicating, via the parameter, that the link path between the first and second apparatuses is LOS if the difference or the ratio between the first and second characteristics is equal to or below a threshold value.
 28. The method of claim 27, wherein the first and second characteristics and the threshold value are adjusted based on a factor.
 29. The method of claim 28, wherein the factor is based on at least one of a cross-polarization number or polarization coefficients. 